Elina Svitolina also won her second game at the WTA Finals on Wednesday. The defending champion was too strong for Simona Halep in the purple group and is thus already certain of a place in the semi-finals.
It became 7-5 and 6-3 on the hard court in Shenzhen, China. In her first game, Svitolina had already won against Karolína Plísková without losing a set.
Plísková hunts later in the day for her first victory against US Open winner Bianca Andreescu, who lost her first match to Halep and is therefore also without a win.
Kiki Bertens is one of the four players in the red group. She was allowed to participate on Tuesday after Naomi Osaka dropped out injured and immediately stunted by beating world number one Ashleigh Barty.
Bertens also has to beat Belinda Bencic on Thursday to reach the semi-finals. The numbers one two of the groups qualify for the final four.
When title defender Svitolina wins the Finals again, it is only her first tournament victory in 2019. The number eight in the world reached the semi-finals at Wimbledon and the US Open and was not yet in a final this year.